correlator: judge each scene on its own embedding + severity (server-26#80, #95)

intelligence.py writes only the primary scene's embedding and severity to
calls/{id}. _build_context read them back off the call doc, so every
non-primary scene of a multi-scene call was correlated against scene 1's
semantic vector and severity rung: a scene about a different event scored
on the embedding path against the wrong incident, and could inherit a
minor/moderate/major severity it never had, clearing the creation gate on
borrowed weight. Same defect and same fix as the #87 coords leak.

- _build_context / preview_correlation / correlate_call: take embedding and
  severity as params; drop the call_doc.get() fallbacks. A scene that
  passes none has none, and is judged thin on its own signal.
- upload.py: both scene loops pass scene["embedding"] / scene["severity"];
  _correlate_with_consensus forwards them. The no-scene unclassified branch
  passes neither (correct: no scene, judged thin).
- recorrelation_sweep: passes the call doc's stored values explicitly
  (whole-call re-link, link-only, so a borrowed severity cannot create).
- intelligence.py: SCENE DETECTION prompt tightened toward one scene
  (server-26#5, partial) - MULTIPLE only for genuinely separate events,
  "when unsure, one scene", plus a not-a-new-scene list.
- test_incident_identity.py: +2 regression tests mirroring the #87 test.

Full c2-core suite green (295 passed). #5 prompt change is unmeasured -
needs a scoped correlation-only window. Known remaining legs, tracked
separately: llm_correlator._call_block still reads the whole-call
transcript per scene; content-divergence veto skips on a None embedding.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

drb-c2-core/tests/test_incident_identity.py

@@ -254,6 +254,56 @@ async def test_a_scene_with_no_location_does_not_inherit_the_call_docs_pin():
     assert ctx["is_thin_call"] is True
 
 
+@pytest.mark.asyncio
+async def test_a_scene_does_not_inherit_the_call_docs_embedding_or_severity():
+    """
+    server-26#80 / #95. Same shape as the #87 coords leak above:
+    intelligence.py writes only the PRIMARY scene's embedding and severity to
+    calls/{id}. A non-primary scene being correlated must be judged on its own
+    embedding (or none) and its own severity — not the call doc's — or a scene
+    about a different event scores against the wrong incident on the embedding
+    path and can inherit a minor/moderate/major rung it never had, clearing the
+    creation gate on borrowed weight.
+    """
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_get = AsyncMock(
+            return_value={"embedding": [0.1] * 1536, "severity": "major"}
+        )
+        mock_fstore.collection_list = AsyncMock(return_value=[])
+        ctx = await _build_context(
+            call_id="call-scene-2", units=None, vehicles=None, cleared_units=None,
+            location_coords=None, reference_time=NOW,
+            system_id="sys-1", talkgroup_id=383, talkgroup_name=DISPATCH_TG,
+            tags=[], incident_type="police", location=None,
+            reassignment=False, create_if_new=True,
+            embedding=None, severity=None,
+        )
+    assert ctx["call_embedding"] is None
+    assert ctx["call_severity"] == "routine"
+    assert ctx["is_thin_call"] is True
+
+
+@pytest.mark.asyncio
+async def test_a_scene_is_judged_on_its_own_embedding_and_severity():
+    """The other half of #80/#95: the scene's own values are what land in ctx."""
+    scene_vec = [0.9] * 1536
+    with patch("app.internal.incident_correlator.fstore") as mock_fstore:
+        mock_fstore.doc_get = AsyncMock(
+            return_value={"embedding": [0.1] * 1536, "severity": "routine"}
+        )
+        mock_fstore.collection_list = AsyncMock(return_value=[])
+        ctx = await _build_context(
+            call_id="call-scene-2", units=None, vehicles=None, cleared_units=None,
+            location_coords=None, reference_time=NOW,
+            system_id="sys-1", talkgroup_id=383, talkgroup_name=DISPATCH_TG,
+            tags=[], incident_type="police", location=None,
+            reassignment=False, create_if_new=True,
+            embedding=scene_vec, severity="major",
+        )
+    assert ctx["call_embedding"] == scene_vec
+    assert ctx["call_severity"] == "major"
+
+
 @pytest.mark.asyncio
 async def test_a_bare_number_never_becomes_an_incident_location_or_title():
     inc = await _create(tags=["flames"], location="49", coords=None,